1. Field of the Invention:
This invention relates to a heat exchanger core and a method for the production thereof. More particularly, this invention relates to a heat exchanger core having a core part thereof brazed by the use of a flux of potassium fluoroaluminate complex, which heat exchanger core is made of an aluminum material and therefore is enabled to obviate the necessity for application of a coating subsequent to the brazing and to a method for the production thereof.
2. Description of the Prior Art:
In recent years, the heat exchangers such as radiators for automobiles and condensers for car coolers use an aluminum material (aluminum or aluminum alloy) in their core parts for the purpose of reduction in weight.
In the heat exchanger made of an aluminum material, used as a condenser in a car cooler, for example, the core part thereof is produced by molding its heat transfer fins with an aluminum material clad with a brazing filler and its tube with an aluminum material, fitting the components to each other with the aid of a jig, for example, and brazing them. As is widely known, in the brazing of parts of an aluminum material, an aluminum oxide coating of a high melting point formed on the surface of the aluminum material is required to be removed from the positions destined to undergo brazing. Unless the brazing is carried out under special conditions in a vacuum or in an atmosphere of inert gas (inevitably by the use of an expensive apparatus), there is followed a practice of applying a flux for the removal of aluminum oxide at least on the positions expected to undergo brazing in advance of the brazing. The flux heretofore used for this purpose has been a mixture of inorganic chlorides (such as for example, alkali metal chlorides and alkaline earth metal compounds). Since such water-soluble compounds by nature are liable to corrode aluminum in the presence of water, however, the core part of the heat exchanger assembled by brazing has inevitably to be subjected to a cleaning work for the removal of water-soluble flux subsequently to the brazing.
Recently, to take the place of the conventional flux of inorganic chlorides, NOCOROC flux (Registered trademark of Alcan Research and Development Limited.) (potassium fluoroaluminate complex) has been proposed and adopted for actual use. This NOCOROC flux possesses a characteristic property of remaining non-hygroscopic prior to brazing and becoming substantially water-insoluble subsequently to brazing and, at the same time, another characteristic property of assuming, while in a fused state, reactivity at a temperature below the melting point of the brazing filler and consequently functioning as a flux for aluminum oxide and remaining unreactive to aluminum (Japanese Patent Publication SHO No. 58(1983)-27,037). When the brazing is effected by the use of NOCOROC flux, therefore, the phenomenon of the corrosion of aluminum by the residual flux experienced by the conventional flux of inorganic chlorides is substantially eliminated.
Even when the heat exchanger undergoes the brazing by the use of this NOCOROC flux, the practice of applying a coating thereon after the brazing work is still persisting. In this case, however, the NOCOROC flux exhibits no corrosiveness to the aluminum material as already described. In fact, in the bench test conducted by me, the heat exchanger assembled by brazing by the use of the NOCOROC flux has shown substantially no discernible difference in corrosion-proofness between the presence and absence of the coating. It has thus been ascertained to me that the necessity for applying the coating arises rather from the standpoint of mainly repressing the haze due to the gloss of the aluminum material and enhancing the commercial value of the heat exchanger as a whole than from the standpoint of improving the corrosion-proofness of the heat exchanger.
In view of the true state of affairs described above, I have concluded it extremely uneconomical to apply a coating on the heat exchanger solely for the purpose of repressing glaring and enhancing commercial value and have made efforts to develop a heat exchanger enabled to obviate the necessity for the step of coating which is so uneconomical as described above and greatly elongates the time required for the production of the heat exchanger.
An object of this invention, therefore, is to provide a heat exchanger core excellent in glare-proofness and a method for the production thereof.
Another object of this invention is to provide a heat exchanger core assembled by brazing by the use of NOCOROC flux, which heat exchanger core possesses sufficiently high glare-proofness without requiring a coating to be applied on the surface portions thereof, and a method for the production thereof.
Yet another object of this invention is to provide a heat exchanger core which does not require application of a coating and which, therefore, is less expensive and permits a cut in the time required for production.